Computer Modelling of Water
Distribution Networks
N.Trifunović, Associate Professor
UNESCO-IHE
Delft, The Netherlands
N. Trifunovic Chapter 0: Module Introduction
4
About my CareerEDUCATION
BSc Civil Engineering (1984) (Faculty of Civil Engineering, University of
Belgrade, Yugoslavia),
MSc in Hydraulic Engineering (1990) (Faculty of Civil Engineering,
University of Belgrade, Yugoslavia)
PhD on reliability assessment of WDN (2012) (Faculty of Civil Engineering
and Geosciences, Delft University of Technology, the Netherlands)
SPECIALISATION
Water supply engineering (urban water distribution, computer modelling)
EXPERIENCE
Over 25 years of professional and academic experience in planning,
design, implementation, and O&M of urban water transport and distribution
systems.
Worked as researcher, water supply company development engineer and
lecturer at UNESCO-IHE since 1990. Current position: Associate
Professor. Recent experience in design and moderation of innovative
learning programmes.
N. Trifunovic Chapter 0: Module Introduction
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About my Work
TEACHING
Water Transport and Distribution: general aspects, hydraulic performance,
operation and maintenance, development and application of hydraulic
models.
Applied hydraulics, Unit Operations (Sedimentation), Engineering Economy
On-line programme in Water Distribution
RESEARCH
Reliability assessment of water distribution systems.
Optimisation of water distribution system operation.
PROJECTS
Director of capacity building projects (Mozambique, South Africa, Ghana).
Team member in training, advisory and consulting assignments in water
distribution in various countries in Africa, Asia and Middle East.
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Contents
• Principles
• Main Features
• Classification
• Designer’s Tips
• New Generation
• Further Information
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Main DefinitionsSteady and Uniform Flow
v1 v2
1 2
)(
2
)(
1
)(
2
)(
12211 tttt
vvvv
Steady flow in a pipe of constant
diameter is at the same time uniform.
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V
Mass Conservation LawThe Continuity Equation
Qinp Qoutt1 V1
t
VQQ outinp
After t ...
Qinp Qoutt2
V2
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Mass Conservation LawThe Continuity Equation
Q1
Qn
Node ‘n’
Q2
Q3
j
i
ni QQ1
0
Q1- Q2+ Q3= Qn
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Energy Conservation LawThe Bernoulli Equation
EEE 21
1 2
becomes:
Eg
v
g
pZ
g
v
g
pZ
22
2
222
2
111
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Grade LinesEnergy, Hydraulic
1 2
Reference level
Z2Z1
g
p2
g
p1
g2
v2
2
g2
v2
1
E1
H1 E2
H2
v
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Energies, HeadsSummary
2
Reference level
Z2
g
p2
g2
v2
2
E2
H2
Elevation Head (potential)
Pressure Head
Piezometric Head
Energy Head (total)Velocity Head (kinetic)
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Energies, HeadsWater Distribution Practice
2
Reference level
Z2
g
p2
H2
Elevation
Pressure
Head
Velocity head becomes relevant
only for velocities well above 1
m/s (example: pumping stations)
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Hydraulic GradientSlope of The Hydraulic Grade Line
Q1
E1S1
L
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Flow rate in pipes under
pressure is related to the
hydraulic gradient!
Hydraulic GradientSlope of The Hydraulic Grade Line
L
ES
Q2
E2S2
L
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Hydraulic LossesFriction, Minor
E
Q
S
L
E results from a friction between
the water and the pipe wall,
and/or a turbulence developed by
obstructions of the flow.
mf n
m
n
fmf QRQRhhE
hf,m = Friction, Minor loss (respectively)Rf,m = Pipe resistanceQ = Flownf,m = Exponents
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Friction LossesDarcy-Weisbach
2
5
2
52 1.12
8Q
D
LQ
gD
LQRh fn
ff
λ = Friction factor (-)L = Pipe length (m)D = Pipe diameter (m)Q = Pipe flow (m
3/s)
or proportional to the kinetic energy:
g
v
D
Lh f
2
2
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Friction FactorColebrook-White
λ = Friction factor (-)Re = Reynolds number (-)k = Absolute roughness (mm)D = Pipe diameter (mm)
Simplified form of Barr (error ±1%):
D
k
7.3Re
51.2log2
1
D
k
7.3Re
1286.5log2
189.0
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Reynolds Number
v = Flow velocity (m/s)D = Pipe diameter (m)ν = Kinematic viscosity (m
2/s)
vDRe
Kinematic viscosity:
5.1
6
5.42
10497
T Temperature,T(ºC)
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Laminar flowThe Reynolds number falls under 2000
Transitional zoneThe Reynolds number falls between 2000 and 4000
Turbulent flowThe Reynolds number is above 4000 with two zones:
1. Zone of transitional turbulence
2. Zone of developed (or rough) turbulence
Flow Regimes
For laminar flow:
Re
64
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Flow Regimes
D
k
7.3Re
1286.5log2
189.0
For transitional zone:
89.0Re
1286.5log2
1
For zone of transitional turbulence:
D
k
7.3log2
1
For zone of developed turbulence:
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The Moody Diagram
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Absolute Roughness
Pipe material
k
(mm) Asbestos cement Galvanised/Coated cast iron Uncoated cast iron Ductile iron Uncoated steel Coated steel Concrete Plastic, PVC, PE Glass fibre Brass, cooper, lead
0.015 - 0.03 0.03 - 0.15 0.15 - 0.6 0.03 - 0.06 0.015 - 0.06 0.03 - 0.15 0.06 - 1.5 0.02 - 0.05
0.06 0.003
Source: Wessex Water, 1993
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The Best Formula?
2
51.12Q
D
Lh f
852.1
87.4852.1
68.10Q
DC
Lh
hw
f
2
3/16
229.10Q
D
LNh f
Darcy-Weisbach
(the most accurate)
Hazen-Williams
(straight-forward)
Manning
(straight-forward)
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Hazen-Williams Factors
Source: Bhave, 1991
Pipe material / D (mm)
75
150
300
600
1200
Uncoated cast iron Coated cast iron Uncoated steel Coated steel Galvanised iron Uncoated asbestos cement Coated asbestos cement Concrete, min. values Concrete, max. values Prestressed concrete PVC, brass, cooper, lead Wavy PVC Bitumen/cement lined
121 129 142 137 129 142 147 69 129
- 147 142 147
125 133 145 142 133 145 149 79 133
- 149 145 149
130 138 147 145
- 147 150 84 138 147 150 147 150
132 140 150 148
- 150 152 90 140 150 152 150 152
134 141 150 148
- - -
95 141 150 153 150 153
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Manning Factors
Source: Bhave, 1991
Pipe material
N
(m-1/3
s) PVC, brass, lead, copper, glass fibre Prestressed concrete Concrete Welded steel Coated cast iron Uncoated cast iron Galvanised iron
0.008 - 0.011 0.009 - 0.012 0.010 - 0.017 0.012 - 0.013 0.012 - 0.014 0.013 - 0.015 0.015 - 0.017
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Source: Prof. V.L. Snoeyink, University of Illinois
Friction LossesCorrosion from Magnesium Silicate
What is the right roughness factor (diameter)?
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Friction LossesSummary
Choice of adequate roughness value is more
important than the choice of the friction formula.
In theory, the friction losses grow by:•increase of discharge
•increase of pipe roughness
•reduction of pipe diameters
•increase of pipe lengths
•decrease of water temperature
In practice, this happens by:•higher consumption or leakage
•corrosion growth
•network expansion
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Minor Losses
Q1
E1
L
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Minor Losses
Q2
E2
L
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ξ = Minor loss factor (-) D = Pipe diameter (m) Q = Pipe flow (m
3/s)
or proportional to the kinetic energy:
v is the velocity downstream the
obstruction.
g
vhm
2
2
2
4
2
42 1.12
8Q
DQ
gDQRh mn
mm
Minor LossesGeneral Formula
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Minor Loss FactorsValve Characteristics (1)
Source: Erhard
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Minor Loss FactorsElbows, Bends, Knees
Source: KSB
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Minor Loss FactorsBranches
Source: KSB
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Minor Loss FactorsEnlargers, Reducers
Source: KSB
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Minor Loss FactorsInlets, Outlets
Source: KSB
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Minor LossesSlope of The Hydraulic Grade Line
Q
E
L
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Minor LossesSlope of The Hydraulic Grade Line
L
ES
Q
E
L
S
Substantial minor losses are measured
only if the flow velocity is high or/and
there is a valve throttling in the system.
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Single Pipe CalculationBasic Parameters
Q
L
D
H
k
T
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Single Pipe CalculationDerived Parameters
Q
L
D
H
k
T
S
vυ
Reλ
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Single Pipe CalculationStandard Input Parameters
L
k
T
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Single Pipe CalculationPipe Pressure
Q
L
D
H=?
k
T
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Single Pipe CalculationMaximum Pipe Capacity
Q=?
L
D
H
k
T
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Single Pipe CalculationOptimal Diameter
Q
L
D=?
H
k
T
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Single Pipe CalculationPipe Pressure
Q
L
D
H=?
k
T
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Single Pipe CalculationPipe Pressure
24
D
Qv
5.1
6
5.42
10497
T
vDRe
D
k
7.3Re
1286.5log
25.0
89.0
2
2
52
8Q
gD
Lh f
L
hS
f
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Single Pipe CalculationMaximum Pipe Capacity
Q=?
L
D
H
k
T
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Single Pipe CalculationMaximum Pipe Capacity
Q=?
L
D
H
k
T
D
k
7.3Re
1286.5log
25.0
89.0
2
vDRe
24
D
Qv
Iterative calculation is necessary!
L
gDhQ
f
8
52
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Single Pipe CalculationMaximum Pipe Capacity
4
2DvQ
5.1
6
5.42
10497
T
Assume v (1 m/s)
vDRe
D
k
7.3Re
1286.5log
25.0
89.0
2
gDSv
2
L
hS
f
vcal=vassNo
YesStart
End
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Single Pipe CalculationMaximum Pipe Capacity
Iteration 1: v = 1 m/s
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Single Pipe CalculationMaximum Pipe Capacity
Iteration 2: v = 1.59 m/s
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Single Pipe CalculationMaximum Pipe Capacity
Iteration 3: v = 1.60 m/s
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Single Pipe CalculationOptimal Diameter
Q
L
D=?
H
k
T
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Single Pipe CalculationOptimal Diameter
L
H
D
k
7.3Re
1286.5log
25.0
89.0
2
vDRe
Iterative calculation is necessary!
Q D=?
k
T
52
28
gh
LQD
f
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Single Pipe CalculationOptimal Diameter
5.1
6
5.42
10497
T
Assume v (1 m/s)
vDRe
D
k
7.3Re
1286.5log
25.0
89.0
2
gDSv
2
L
hS
f
vcal=vassNo
Yes
StartEnd
v
QD
4
v
QD
4
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Single Pipe CalculationOptimal Diameter
Iteration 1: v = 1 m/s
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Single Pipe CalculationOptimal Diameter
Iteration 2: v = 2.29 m/s
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Single Pipe CalculationOptimal Diameter
Iteration 3: v = 1.84 m/s
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Single Pipe CalculationOptimal Diameter
Iteration 4: v = 1.95 m/s
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Single Pipe CalculationOptimal Diameter
Iteration 5: v = 1.92 m/s
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Single Pipe CalculationOptimal Diameter
Iteration 6: v = 1.93 m/s
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Branched SystemsSupply at One Point
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Branched SystemsSupply at One Point
• Pipe Flows
– For known nodal demands, the rates can be easily determined (the
Continuity Equation).
– Flow directions are known based on the pipes’ connectivity.
• Velocities
– For known flow rates and pipe diameters can be easily determined.
– The velocity directions are known.
• Pressures
– If there is at least one point of reference (fixed) piezometric head, the
pressures can be easily determined from known nodal elevations.
– The fixed piezometric head should be specified either at the source or
a node where certain (minimum) pressure is to be maintained
• Hydraulic calculation
– It follows the principles of single pipe calculation for pipe pressures and
optimal diameters (at fixed hydraulic gradient).
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Single SourceDiameters & Nodal Elevations
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Single SourceFlows & Nodal Demands
24
D
Qv
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Single SourceVelocities & Nodal Demands
g
v
D
Lh f
2
2
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Single SourceHead Losses & Piezometric Heads
2
Reference
level
Z2
g
p2
H2
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Single SourceHead Losses & Pressures
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Single SourceSpreadsheet Application
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Single SourceSpreadsheet Application
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Branched SystemsSupply at Several Points (1)
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Branched SystemsSupply at Several Points (2)
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Branched SystemsSupply at Several Points
• Pipe Flows
– For known nodal demands, the rates can be partially determined.
– Flow rates & directions in the pipe routes connecting the sources
depend on the piezometric heads at the sources and the distribution of
nodal demands.
• Velocities
– Also partially known.
• Pressures
– Conditions are the same as in case of the single source, once the
flows and velocities have been determined.
• Hydraulic calculation
– Single pipe calculation can only partially solve the system.
– Additional condition is necessary.
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Multiple SourceSource 1 (60 msl) & Source 11 (75 msl)
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Multiple SourceDemand Shifting From Node 8 to Node 4
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Multiple SourceSource 1 (60 msl) & Source 11 (70 msl)
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Looped Networks
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Looped Networks
• Pipe Flows
– Flow rates and directions are unknown.
• Velocities
– The velocities and their directions are known only after the flows have
been calculated.
• Pressures
– Conditions are the same as in case of branched networks once the
flows and hydraulic losses have been calculated for each pipe.
• Hydraulic calculation
– The equations used for single pipe calculation are not sufficient.
– Additional conditions have to be introduced.
– Iterative calculation process is needed.
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Branched NetworkDiameters & Nodal Elevations
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Looped NetworkDiameters & Nodal Elevations
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Branched NetworkFlows & Nodal Demands
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Looped NetworkFlows & Nodal Demands
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Branched NetworkHead Losses & Pressures
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Looped NetworkHead Losses & Pressures
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Kirchoff’s Laws
Flow continuity at junction of pipesThe sum of all ingoing and outgoing flows in each node equals
zero (SQi = 0).
Head loss continuity at loop of pipesThe sum of all head-losses along pipes that compose a
complete loop equals zero (SΔHi = 0).
• Hardy Cross Methods
– Method of Balancing Heads
– Method of Balancing Flows
• Linear Theory
• Newton Raphson
• Gradient Algorithm
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Hardy CrossMethod of Balancing Heads
Step 1Arbitrary flows are assigned to each pipe; (SQi = 0).
Step 2Head-loss in each pipe is calculated.
Step 3The sum of the head-losses along each loop is
checked.
Step 4If SΔHi differs from the required accuracy, a flow
correction δQ is introduced in loop ‘i’.
Step 5Correction δQ is applied in each loop (clockwise or anti-
clockwise). The iteration continues with Step 2
n
j j
j
n
j
j
j
Q
H
H
Q
1
1
2
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87
Hardy CrossMethod of Balancing Heads - Example
Iteration 1
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Hardy CrossMethod of Balancing Heads - Example
Iteration 2
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Hardy CrossMethod of Balancing Heads - Example
Iteration 3
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Hardy CrossMethod of Balancing Heads - Example
Iteration 4
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Hardy CrossMethod of Balancing Heads - Example
Iteration 7
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Hardy CrossMethod of Balancing Flows
Step 1Arbitrary and unique piezometric head is assigned to
each node; head-loss in each pipe is determined from
these piezometric heads.
Step 2Flow in each pipe is calculated.
Step 3Flow continuity is checked in each pipe junction.
Step 4If SQi differs from the required accuracy, a piezometric
head correction δH is introduced in node ‘i’.
Step 5Correction δH is applied in each node and new head
losses determined. The iteration continues with Step 2
n
i i
i
n
i
i
i
H
Q
Q
H
1
1
2
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Hardy CrossMethod of Balancing Flows - Example
Iteration 1
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Hardy CrossMethod of Balancing Flows - Example
Iteration 2
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Hardy CrossMethod of Balancing Flows - Example
Iteration 3
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Hardy CrossMethod of Balancing Flows - Example
Iteration 4
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Hardy CrossMethod of Balancing Flows - Example
Iteration 8
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Linear Theory
UQQQRRH mf )(51.12
)(
D
QDLU
01
n
j
iji QQ
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99
Linear TheoryJunction of Three Pipes (1)
iiii QQQQ 312
i
i
i
i
i
i
i QU
HH
U
HH
U
HH
3
3
1
1
2
2
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100
Linear TheoryJunction of Three Pipes (2)
i
i
i
i
i
i
i QU
HH
U
HH
U
HH
3
3
1
1
2
2
i
i
i
i
i
i
i
iii
QU
H
U
H
U
H
U
H
U
H
U
H
3213
3
2
2
1
1
013
1
3
1
j ij
i
j ij
j
iU
HU
HQ
3
1
3
1
1
j ij
j
i
ij
j
i
U
QU
H
H
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101
Linear TheoryGeneral Format
n
j ij
i
n
j ij
j
iiiU
HU
HQHf
11
1)(
)(1
ii
n
j
iji HfQQ
ij
ij
ijU
HQ
System of linear equations that is equal to the number of
nodes in the network, ‘m’, creates a matrix ‘m×n’ where ‘n’
is the maximum number of pipes that can meet in any
junction of the network. This system can also be solved by
the Newton Raphson method.
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102
Newton Raphson MethodGeneral Format
)('
)()(
)()()1(
k
i
k
ik
i
k
iHf
HfHH
n
jk
ij
k
i
n
jk
ij
k
j
i
k
iU
HU
HQHf
1)(
)(
1)(
)(
)( 1)(
n
jk
ij
k
iU
Hf1
)(
)( 1)('
n
jk
ij
n
j
n
jk
ij
k
ik
ij
k
j
i
k
i
k
i
U
UH
U
HQ
HH
1)(
1 1)(
)(
)(
)(
)()1(
1
1
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103
Iterative Process
Step 1 - PreparationSetting of initial values for pipe flows and nodal piezometric heads in the
1st iteration; calculation of U-values.
Step 2 – Internal cycleIterations of the piezometric heads; the calculation is repeated until H(k+1) -
H(k) < εH in each node, or the number of iterations has reached the
maximum specified number.
Step 3 – External cycleCalculation of pipe flows Qi = ΔHi/Ui. Check the flows in each node (Q(l+1) -
Q(l) < εQ ). ‘No’: recalculation of the U-values with the flows from the
current iteration and restart of the iterative process in Step 2. ‘Yes’: Step 4
Step 4 – Determination of pressures The iterative process is finished; the pressures are calculated for each
node based on its elevation and the final value of the piezometric head.
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104
Linear TheorySpreadsheet Example
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105
Fixed Demand Conventional Approach
Reference level
Z
g
p2
g
p1
ΔH1
Q
S1
S2ΔH2
Q=const
ΔH1=ΔH2
S1=S2
t1
t2
Fixed head point(s) influence(s)
the pressure distribution in a
system of fixed demands.
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106
Q1
S1
L
Fixed Demand Pressure Change (1)
t1
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107
Q2
S2
L
Fixed Demand Pressure Change (2)
t2
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108
Q3
S3
L
Fixed Demand Pressure Change (3)
t3
Q1=Q2=Q3
S1=S2=S3
Any specified demand is
satisfied while the pressure
can have negative value.
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109
Pressure Related Demand Pressure Dependant Leakage
2
51.12Q
D
Lh f
Source: Wessex Water, 1993
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110
Q1
S1
L
Pressure Related Demand Pressure & Demand Change (1)
t1
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Q2
S2
L
Pressure Related Demand Pressure & Demand Change (2)
t2
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Q3
S3
L
Pressure Related Demand Pressure Change (3)
t3
Q1>Q2>Q3
S1>S2>S3
The specified demand
gradually drops based
on the pressure drop.
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Pressure Related Demand Similarity With The Discharge Through Orifice
gA
Qhm
22
2
ghCAQ 2
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Pressure Related Demand Practical Application
Source: KIWA, 1993
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Types of Hydraulic Calculation
• Demand-Driven– Any nodal demand is satisfied
– Pressures can be negative
• Pressure-Driven– Nodal demand depends on the pressure
– Pressures can never be negative
• Optimisation (Genetic Algorithms)
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Demand Driven CalculationRegular Supply
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Demand Driven CalculationRepair Pipe 6-9
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Pressure Driven CalculationRegular Supply
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Pressure Driven CalculationRepair Pipe 6-9
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Types of Models
• For Network Design– Major pipes and valves, reservoirs and pumps
– Not for tertiary networks
• For Network Operation and
Maintenance (GIS)– Calamities
– Flushing
– Water quality
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Network Model of Amsterdam
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Modelling ProcessMain Steps
1. Input data collection
2. Network schematisation
(skeletonisation)
3. Model building
4. Model testing
5. Problem analysis
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Input Data CollectionMain Categories
1. General data
2. Water demand
3. Network layout
4. Network operation and monitoring
5. Network maintenance
6. Water company organisation
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Input Data CollectionGeneral Data
1. Layout of the system – pipe routes and
junctions; location of the main components.
2. Topography - ground elevations in the area of the
system; some specific natural barriers.
3. Type of the system - distribution scheme: gravity,
pumping, combined; role of each system
component.
4. Population - distribution and estimated growth.
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Input Data CollectionWater Demand
1. Demand categories present in the system: average
domestic consumption, industry, tourism, etc.
2. Patterns of variation: daily, weekly, and seasonal.
3. Type of domestic water use: direct supply, roof
tanks, etc.; average household size, habits with
respect to water use.
4. Demand forecasting.
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Input Data CollectionNetwork Layout – Nodes and Pipes
1. Nodes (discharge points) - concerns predominantly the
supply points of at least a few hundred consumers or major
industry. Relevant for each point are:
- location (X,Y) in the system,
- ground elevation (Z), and
- average consumption and dominant categories.
2. Pipes - concerns predominantly the pipes D > 80-100 mm.
Relevant for each pipe are:
- length,
- diameter (internal),
- material and age,
- assessment of corrosion level (description of roughness)
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Input Data CollectionNetwork Layout - Storage
1. Service reservoirs - type (ground, elevated),
capacity, minimum and maximum water level,
shape (e.g. described through the volume-depth
curve), inlet/outlet arrangement.
2. Individual roof tanks (where applicable) - type
and height of the tank, capacity, inflow/outflow
arrangements, average number of users per
house connection, description of house
installations (existence of direct supply in the
ground floor).
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Input Data CollectionNetwork Layout – Pumping Stations and Others
1. Pumping stations - number and type (variable,
fixed speed) of pumps; duty head and flow and
preferably the pump characteristics for each unit;
age and condition of pumps.
2. Others - description of appurtenances that may
significantly influence the system operation (e.g.
valves, measuring equipment, etc.)
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Input Data CollectionNetwork Operation and Monitoring
Important and preferably simultaneous measurements:
• The pressure in a number of points covering the
entire network
• Level variations in the service reservoirs and roof
tanks (where applicable)
• Pressures and flows in the pumping stations
• The flows in a few main pipes in the network
• Valve operation (where applicable)
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Network SchematisationBenefits
Advantages:
• It saves computer time.
• It allows model building in steps i.e. easier tracing
of possible errors.
• It provides a clearer picture about global operation
of the system.
Reduction of the model size with acceptable
reduction of the model accuracy.
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Network SchematisationDo’s and Don’t’s
1. Combination of a few demand points close to each
other into one node.
2. Exclusion of a hydraulically irrelevant part of the
network such as branches and dead ends at the
borders of the system.
3. Neglecting small pipe diameters.
4. Introduction of equivalent pipe diameters.
5. Omit demand of excluded parts of the network.
6. Elimination of major loops.
7. Neglect the impact of existing pumps, storage and
valves.
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Network SchematisationPipe Elimination
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Network SchematisationElimination of Small Pipes
1. When laying perpendicular to the usual direction of
flow.
2. If conveying flows with extremely low velocities.
3. When located in the vicinity of large diameter pipes.
4. When located faraway from the supply points.
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Model BuildingMain Information
1. Junctions
• sources
• nodes
• reservoirs
2. Links
• pipes
• pumps
• valves
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Model BuildingInformation for Junctions
1. Sources: identification, location and elevation of water
surface level.
2. Nodes: identification, location and elevation, average
demand and pattern of demand variation.
3. Reservoirs: identification, position, top & bottom water
level, description of the shape (cross-section area, either
the volume-depth diagram), initial water level at the
beginning of the simulation, inlet/outlet arrangement.
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Model BuildingInformation for Links
1. Pipes: identification, length, diameter, description of
roughness, minor loss factor .
2. Pumps: identification, description of pump
characteristics, speed, operation mode .
3. Valves: identification, type of valve, diameter, head-
loss when fully open, operation mode .
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Input Data CollectionNetwork Layout - Pipes
1. Water quality parameters:
– initial concentrations,
– patterns of variation at the source,
– decay coefficients, etc.
2. Simulation run parameters:
– duration of the simulation,
– time intervals,
– accuracy,
– preferred format of the output, etc.
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Demand ModellingGraphical Method
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Demand ModellingCalculation Method
qA = QA / (L1-2 + L4-5+L1-4+L2-5)
qB = QB / (L2-3+L5-6+L2-5+L3-6)
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Demand ModellingCalculation Method
Q1-2= qA×L1-2
Q4-5 = qA×L4-5
Q1-4 = qA×L1-4
Q2-5,A = qA×L2-5
Q2-3= qB×L2-3
Q5-6 = qB×L5-6
Q2-5,B = qB×L2-5
Q3-6,A = qB×L3-6
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Demand ModellingCalculation Method
Q1 = (Q1-2+Q1-4) / 2
Q2 = (Q1-2+Q2-3+Q2-5,A+Q2-5,B) / 2
Q3 = (Q2-3+Q3-6) / 2
Q4 = (Q1-4+Q4-5) / 2
Q5 = (Q4-5+Q5-6+Q2-5,A+Q2-5,B) / 2
Q6 = (Q5-6+Q3-6) / 2
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Model TestingValidation and Calibration
• the model has a logical response to the altering of the
input data; the simulation runs are in this case functioning
in the model validation,
• the model is behaving in relation to the real system;
comparison of the calculation results with the hydraulic
measurements is part of the model calibration.
Once the first simulation run has been completed, the
immediate concern is whether the results match reality. In
this phase, several runs have to be executed which must
confirm that:
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Model TestingValidation and Calibration Errors
There can be different reasons why the validation and
calibration cannot be achieved. The input file can be
accepted by the programme as correct in syntax, but:
• Some input data were (badly) estimated, because the real values
were not known.
• The network was transferred to the model with some typing errors or
data was omitted.
• The format of the input file was incorrect but the error was not
(clearly) defined in the error library: e.g. too high a calculation
accuracy, insufficient maximum number of iterations, impossible
operation mode specified, etc.
• The field measurements used for the model calibration were
inaccurate.
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Problem AnalysisPossibilities
1. Selection of optimal pipe diameters for a given layout and demand
scenario
2. Selection of optimal models for pumps
3. Selection of optimal position, elevation and volume of the reservoir(s)
4. Optimisation of the pump scheduling (to minimise energy consumption)
5. Optimisation of the reservoir operation (water depth variation)
6. Optimisation of the valve operation
7. Simulation of fires
8. Planning of pipe flushing in the system
9. Analysis of failures of the main system components (risk assessment)
10. Analysis of water quality in the system (chlorine residuals, water age
and mixing of water from various sources)
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Computer Modelling SoftwareMain Features
1. PC based applications.
2. Allow extended period hydraulic simulations.
3. Posses integrated module for water quality
simulations.
4. Can handle virtually unlimited size of network.
5. Have excellent graphical interface for
presentation of results.
6. Have link/interface with GIS.
7. Have integrated modules that allow on-line
operational decisions
8. Have built-in optimisation algorithms.
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Present MarketSome Offers
1. EPANET 2 (US Environmental Protection Agency)
2. WaterCAD© (Bentley, USA)
3. WaterGEMS© (Bentley, USA)
4. InfoWorks WS© (Wallingford Software, UK)
5. SynerGEE Water© (Advantica Stoner, USA)
Price Range: 0 to approx. 60,000 USD
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Network ModelsEpanet 2
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Network ModelsInfoWorks WS
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WaterGEMS©
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More Information
• US Environmental Protection Agency
– www.epa.gov (EPANET 2)
• Bentley
– www.bentley.com (WaterCAD, WaterGEMS)
• Wallingford Software
– www.wallingfordsoftware.com (InfoWorks WS)
• Advantica Stoner
– www.advanticastoner.com (SynerGEE Water)
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Model Input - Pumps
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Model Input - Demands
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Model Layout
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Model Data Filtering
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Tracing of Connectivity
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Demand Allocation
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Demand Concentration
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Model Link With GIS
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Model Labels
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Longitudinal Profiles
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Pump Energy Costs
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Simulation Run Parameters
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1 day, 15 min. time step
38.500 pipes in 6 min.
PIII, 1.2 MHz Notebook
Network Model of Amsterdam
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Model Calibration
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Valve Operation
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Operation of Storage and Pumps
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Time Series Results
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Water Quality Model
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Sediment Transport Assessment
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Source Tracing
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The Best Software?
1. Cheaper software often solves the same problems as the more expensive one.
2. It is the quality of input data rather than the quality of software that is a limiting factor: what goes in, goes out!
3. Model calibration is essential and requires properly working monitoring equipment.
4. Advanced software will be fully utilised only in an advanced water distribution system.
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Friction LossesIron Corrosion
Source: Prof. V.L. Snoeyink, University of Illinois
Percentage of the original cross-section (the same network)
What is the right roughness factor (diameter)?